If it's a real Enfield #5 Jungle Carbine, and it was mine, here's what I would do:

The foreend cap is the biggest challenge in recreating a forestock. I'd try to save the original stock, and splice in a replacement piece to replace what was cut off. You could hide the splice under the band. I would not try to fit a #4 stock to a Jungle Carbine, as that provides no real improvement over the present status.

Stocks alone for the #5 fetch crazy prices, but you just might find a busted one for a good price, and get the donor piece you need. Save a search on eBay and Gunbroker.com and be patient. This might take several months.

Get some good pictures to scale and you could have a replica forend cap made on a 3-d printer, paint it flat black and you'd be good to go, or if you know a tinsmith, they could make one for you.

Candyman on this forum had good tutorials on repairs of this nature. Send him a PM and see if he could help you.

Several of us have an Enfield 5 kicking around, so if you need measurements and pictures for the forestock from the band forward, let us know.

All good things come to those that wait and have cash. You see approximately 1 stock per year on ebay. Sometimes you see a complete stock at gun shows where a gunsmith took it off to switch a sporter/hunting rifle into a nice sturdy black stock. The last complete stock sold for $275 that I saw at the Fond du lac gun show last year. It was gone in the first 30 min of entering the show. Some times the guys get more for the parts than a complete rifle. I got its bolt with a #3 bolt head for $75.

To old to fight and to old to run, a Jar head will just shoot and be done with you.

One other option would be to pick up a complete No. 5 if you can do so at a fair price

That is an interesting idea. Three years ago I got a complete rifle for $300 because the guy put his SSN on the side of receiver to mark his rifle. Bore is like new, and it had no import marks. But due to the scribed SSN, no one wanted it. It sat at the same show for 3 times at $425. On the fourth show I decided to offer $300 and he took the offer. My buddy Timbuktu just shook his head because why does someone need more than 2 of each year for JCs. He refers to me as a JC horder. When I stroke out again I am going to be buried with one.
I use it as my shooter and keep all my nice ones on the rack, so deals are out there, it just takes time and some luck to stumble onto some parts or rifles that a guy or family is letting go at the price that was originally paid 10-15 years ago. At big shows there are always sales where the family sets up to dump the dead collectors goodies-- you just got to beat the dealers to the table
People always want slings, bolts and boltheads, the bands, the rubber butt assy, and also the flash cone. The sock and bayonet are the most sought after.
I think the average price is around $ 450-500 for an import marked example, War years and bring backs lacking the import mark and look like new are going for more in WI. The nuts want $250-350 for an original bayonet. Maybe you can find a cheep 46 or 47 one. I assume the sporter was cheep at around $150. The bolt, cone, and butt plate& pad covers that value. Get a nice JC and see what action & stock is in best condition.

To old to fight and to old to run, a Jar head will just shoot and be done with you.